A bicyclist rides 4.9 km due east, while the resistive force from the air has a magnitude of 3.4 N and points due west. The rider then turns around and rides 4.9 km due west, back to her starting point. The resistive force from the air on the return trip has a magnitude of 4.0 N and points due east.
(a) Find the work done by the resistive force during the round trip.